Long haul trucks must store enough fuel to travel between gas stations during long trips. While diesel gas stations are fairly ubiquitous and can be found throughout the United States, the same cannot be said for other fuel types, including natural gas and compressed natural gas. Natural gas and compressed natural gas can be cheaper than diesel and other current fuels, and some predictions suggest that natural gas will remain relatively inexpensive, at least in part because of the recent abundance of “shale” gas resulting from modern fracking and horizontal drilling technologies. Natural gas also burns cleaner, and there is a fairly significant domestic supply of natural gas.
Despite the advantages, most long haul trucks have not been converted to use or carry natural gas or compressed natural gas. There is a lack of infrastructure with few fueling systems, and few vehicles that use natural gas or compressed natural gas. This has essentially created a chicken-and-egg problem, where trucks cannot convert to natural gas or compressed natural gas because there are too few fueling stations, and there aren't enough fueling stations because there is insufficient demand.
Additionally, in order to obtain an energy equivalent of the diesel tanks that long haul trucks currently use, the volume of compressed natural gas is approximately four times that of equivalent diesel. One cubic foot of compressed natural gas at 3600 psi contains as much energy as two gallons (or 0.27 cubic feet) of diesel fuel. Thus for, the equivalent of 500 gallons (66.84 cubic feet) of diesel fuel, one would need CNG pressurized tanks with a total volume of 250 cubic feet. As a result, the truck would need approximately four times the volume capacity of the diesel fuel tanks currently used in order to get the same range between fuel stops. Equal volume compressed natural gas tanks would provide only about one-fourth the energy and one-fourth the range between refueling stops.